Polymeric materials have one important deficiency which must be overcome before they can be used in various commercial applications. This deficiency is the susceptibility to oxidative and actinic degradation. Many varieties of compounds have been known to be useful as stabilizers of various polymers, but all of them have certain deficiencies which limits the usefulness of such stabilizers. Thus, one class of stabilizers disclosed in the prior art that is related to the compounds of this invention is hindered hydroxybenzoates disclosed in U.S. Pat. Nos. 3,029,276; 3,112,338; 3,206,431 and 3,502,613. British Pat. No. 991,591 also discloses nickel salts of hindered phenolic benzoates.
The compounds of this invention are metal salts of benzoyloxybenzoates. Thus, they are totally different from the various esters of 3,5-dialkyl-4-hydroxybenzoic acids disclosed in the above noted patents and also substantially different from the metal salts of hindered phenolic benzoates. One important difference in the properties between the prior art compounds discussed above and the metal salts of benzoyloxybenzoates of this invention is the improved thermal stability of the instant compounds. This is a very important feature because the polymer substrates which are stabilized with such compounds are subjected to high temperature processing during the various manufacturing stages. Compounds which are not thermally stable will decompose during processing which will result in decreased stabilization effectiveness during the life of the polymer and also may introduce discoloration.
The compounds of this invention also have better gas fading properties and have better water and organic solvent extraction resistance than the prior art compounds.
Furthermore, the compounds of this invention have better color stability to artificial light than the prior art compounds.